An Xplenty cluster is a group of machines (nodes) that is allocated exclusively to your account's users. You can create one or more clusters, and you can run one or more jobs on each cluster. A cluster that you've created remains allocated to your account until you request to terminate the cluster.
When you create a new cluster, you can choose from different cluster sizes (the number of nodes) according to the computing power you require for different types of jobs and packages. Generally speaking, the relationship between the number of nodes and computing power is linear: if a job takes four hours to run a four node cluster, it will take one hour to run on a 16 node cluster.
All accounts include a free sandbox cluster for testing jobs on relatively small amounts data during the package development cycle. Since the sandbox cluster is single-node and neither scalable nor highly available, it is not production grade.
Trial users who haven't selected a billing plan can only use the sandbox cluster during the trial period.